A spectrophotometer including: a) a light source switching mechanism for switching a plurality of light sources by swinging a light source mirror; b) a filter selecting mechanism; c) a diffraction grating rotating mechanism; and d) a controller for determining the operation origins of the three driving mechanisms using a rough origin sensor provided for the diffraction grating rotating mechanism and a photometer. The operation of the controller is to: i) determine an origin of the movement of the filter by making an end of the filter frame to touch a stopper; ii) determine a rough origin of the diffraction grating using the rough origin sensor; and iii) determine an origin of the movement of the light source mirror and a precise origin of the movement of the diffraction grating by detecting the position at which the photometer detects the maximum intensity of light.